U.S. Army Space and Missile Defense Command researchers explore high-energy lasers
By Charles LaMar, SMDC Technical Center
High-energy laser research has been ongoing since the 1960s. But the Army is now getting to the point where demonstration systems are shooting down mortars and unmanned aerial vehicles with high-energy lasers.
“This is a future capability for our Army,” said Keith Jadus, acting director of the lethality portfolio for the Office of the Deputy Assistant Secretary of the Army for Research and Technology. “When you deal with what we call disruptive technology, where the capability is so divergent from how we currently do business, we are required to consider more than just the lethal impacts. We must consider the doctrinal implications on how we fight in the future. Technology such as this creates opportunities to fight a different fight, and can impact the full spectrum of warfare.”
With high-energy lasers, Jadus said there is still a lot to work out.
“We recently had some impressive demonstrations using a commercial laser and supporting beam control, power, and thermal subsystems all integrated onto a mobile military truck, yet we still need to further mature the technology,” he said. “Our laser programs are achieving promising results in the laboratory, and we are developing support subsystems to enable long run-times at these laser’s higher power levels.”
As Army researchers validate the technology, officials remain optimistic about its potential.
The High Energy Laser Mobile Demonstrator, or HEL MD, is the culmination of the Army high-energy laser technology development and demonstration program, according to officials. It is a completely contained HEL weapon demonstrator mounted on an Army truck with a significant track record for engaging and destroying mortars.
The HEL MD will integrate will integrate, in the near future, a more advanced electric laser into its beam control system.
Lethality testing is a crucial component of the Army’s High Energy Laser Program.
“Our goal is to have a demonstrator HEL weapon available in very near term”, said Richard De Fatta, director of the Emerging Technology Directorate at the Army’s Space and Missile Defense Command. “Our lethality team is responsible for acquiring the essential effectiveness data so that we can make the appropriate program decisions at that time.”
In the summer of 2000, the Tactical High Energy Laser, or THEL, shot down its first artillery rocket and began a successful program that lasted several years ending with a kill success against rockets, artillery and mortar greater than 90 percent.
The U.S. Army Space and Missile Defense Command and the Israel Ministry of Defense jointly developed the THEL. Its ultimate destination was intended to be the northern border of Israel. Despite its technical success, officials decided against deployment. THEL relied on toxic chemicals for its operation, which affected system reliability, logistics, cost and safety. However, the program did not end. U.S. Army researchers continue to work on high-energy lasers, known as HELs.
Solid state lasers that relied strictly on electricity for power seemed to be the better solution, but they were not of the technical maturity needed for a weapon. The Joint High Power Solid State Laser, or JHPSSL, program was the answer to the technology shortfall. The JHPSSL program started as a joint effort with the High Energy Laser-Joint Technology Office, the Army and the Air Force. The program achieved its primary objective in 2009 as Northrop Grumman demonstrated a solid-state laser world record power of more than 100 kilowatts for several minutes.
One challenge the research and development teams faced was that the lasers were not rugged enough for Army weapon systems.
The program objectives of JHPSSL were to demonstrate coherence and power. The resulting product of the JHPSSL program was a laboratory device not suitable for the difficult conditions that weapon systems encounter.
The Robust Electric Laser Initiative, or RELI, program addressed the problem.
“The RELI program significantly advanced solid state laser technologies”, De Fatta said. “The Army is confident that RELI technology developments will result in fundamental capability advances for future laser weapon systems.”
The products of this program were to be high-energy laser technologies with the size, weight and ruggedness suitable for development into high-energy laser weapons for multiservice applications.
The new electric lasers operate at much shorter wavelengths and lower powers than their predecessor chemical lasers. The shorter wavelength can result in smaller, more intense laser beams; however, atmospheric interactions and target effects can be substantially different at the shorter wavelength. The shorter wavelength and lower power shifts more performance burden to the beam control system.
The beam control system is the other high tech component of the HEL weapon. The beam control system must precisely point the HEL to the target. The target can be the size of a soft drink bottle and many kilometers away from the laser. The beam control system must point and maintain the beam on the target to a precision of less than a centimeter. In addition, the atmospheric turbulence over these long paths causes the beam to spread. The beam control system must correct for this spreading through the use of potentially complex adaptive optics.
It is the combined effect of the HEL and the beam control system that determines the overall lethality of the weapon. Army lethality scientists must estimate the performance of the beam control system and the HEL and then conduct tests that properly simulate this performance.
SOLID STATE LASER TESTBED
Recognizing the importance of measuring the lethality of HEL weapons, the Army established a facility dedicated to HEL lethality measurements. The Solid State Laser Testbed, or SSLT, is located at the High Energy Laser Systems Test Facility at White Sands Missile Range, N.M. It is a one-of-a-kind Department of Defense asset operated by the U.S. Army Space and Missile Defense Command that enables lethality scientists the capability to conduct both static and dynamic testing.
The SSLT currently consists of two HELs and a beam control system. To make the most effective use of resources, the primary HEL is the JHPSSL built by Northrop Grumman. It was refurbished and relocated to White Sands Missile Range. Officials said the challenge was to locate a laser designed for the laboratory to a relatively remote location in the desert. In addition, the beam control system is the same system built for the THEL program more than 10 years ago. Engineers refurbished and modified it to account for the different wavelength of the JHPSSL. For lethality testing, it is not necessary for the beam control system to operate at the full performance level of a modern tactical beam control system as long as the actual performance is properly characterized. The HEL and the beam control system were successfully integrated, and they have already provided a substantial amount of lethality data.
In static testing, the vulnerability of a target to laser irradiation is assessed in controlled conditions that include basic material, or coupon, testing as well as target testing. Dynamic testing is a more complicated and expensive test. In dynamic testing, the target is flown much like it would be in an actual wartime engagement. The system under test must acquire the target, track the target, point the laser to the target, and then fire the laser. Dynamic testing enables a combined performance measurement of the beam control system and the HEL. Due to the difficulty in measuring beam control performance on a rapidly moving target, static testing is a critical step in the process of making a total performance measurement.
The lethality testing process starts with the identification of the target. A geometric model of the target is created and, if the target is complicated, a failure modes and effects analysis, or FMEA, is accomplished to identify the most promising aimpoints. The FMEA is accomplished in concert with laser interaction physics models. Once these models are constructed, a beam control system model is constructed using the estimated performance parameters of the beam control system. The net result of these steps is a list of the most promising aimpoints that are then tested in a series of static tests. The static tests identify the highest priority aimpoints.
The engagement model is the final step before the dynamic test. It is an end-to-end simulation of an engagement. The actual engagement is typically constrained by the capabilities of the test range, in this case White Sands Missile Range. The engagement model uses the beam control system performance, the lethality data, and the target data to make estimates of the necessary dwell time on the target. The engagement model results are used to plan the details of the dynamic test. The predicted kill time and the actual results are then compared. If the results are within experimental error, then the vulnerability of the target has been verified.
For researchers, this is an ideal description of the process. In reality, one or more of these steps can often not be accomplished due to circumstances beyond the control of the test scientists. A target may be too expensive, a target may not be available, or the test budget may not support a large number of dynamic tests. These constraints put a premium on the use of verified and validated models. The scientists must identify these models early in the process and conduct the tests in the proper manner to provide the confidence needed to rely on these models when there is no test data available.
HEL weapons have captured considerable attention in recent years. Officials said the Army has a plan for development and potential deployment of a laser weapon in the not too distant future.
“This is a great time to be a part of this technology,” De Fatta said.” The Army is well positioned to take advantage of recent technology advances. We are excited about the opportunity to develop, test, and field these new weapon technologies for our warfighters.”
Editor’s note: Charles LaMar is a member of the Army Space and Missile Defense Command’s Technical Center assigned to the Directed Energy Division. Lamar is the program manager for the Army’s Solid State Laser Testbed and has written more than 50 professional papers and publications in the field of high-energy lasers.